The present invention relates to an article exchange apparatus which can be used in an auto-loader having positioning and clamping functions, an auto-loader having an exchange arm, or an automatic tool exchange apparatus of a machine tool.
A conveyor system of a machine tool is known which functions to convey a workpiece from its storage or standby position to its machining position. The machine tool is a clamp or fixture for positioning the workpiece at its correct machining position and for fixing the workpiece so reliably as to allow the workpiece to endure a cutting force during the machining operation. The workpiece is usually positioned, in advance, at its storage or stand-by position. Therefore, a series of fundamental operations are required to simultaneously chuck the workpiece at its storage or stand-by position and chuck a workpiece that is fixed by the aforementioned fixture, to exchange the two workpieces, and then to unload the workpiece which has been machined. That is to say, the following three operational elements are required:
(1) to chuck and unload a workpiece;
(2) to extract another workpiece from its stand-by position and to load the other workpiece; and (3) to exchange the workpieces.
Moreover, these fundamental operations are performed by using respective drive sources, which usually utilize hydraulic or pneumatic pressure. The aforementioned respective drive sources are controlled by electromagnetic change-over valves, which are coupled to such signal generators, e.g. limit switches for detecting the operational ends of the respective movements, as are disposed in a sequence circuit for controlling the respective operations in a predetermined order so that the electromagnetic change-over valves are controlled by the signals of these signal generators.
However, the control method thus far described frequently has a timer disposed in the sequence circuit so that a predetermined locus of movement may not be missed when interchange takes place from one operation to a subsequent operation or so that the reception of the signals of the signal generators may be stabilized to reduce shocks during the starting or stopping of movements. Moreover, it is customary to use a speed adjustor to mechanically weaken such shocks. As a result, the timer of the speed adjustor governs the time period for the series operations of the auto-loader. This causes a problem in that the operating time period (i.e. the non-cutting time period) cannot be made shorter than a predetermined level.
Furthermore, the limit switch and the drive source are frequently mounted on a movable unit, so that wiring and fluid conduits to those apparatus have to be made extendible or rotatable. This raises a further problem in that of damage to such wiring and conduits, due to shock generated by the series operations or by repetition of movement, is increased. This degrades the reliability of the system as a whole.